In many cases spraying a developing first flush leads to good results. The casing soil stays moist and the mushrooms later in the flush are also firm.
However, now the summer is here, it's a good idea to critically examine the growing room climate and the way it is created before resorting to spraying.
After the first picking day of the first flush, often a Sunday or Monday, have a good look at the status of the growing room climate. If the air inlet is 100 % open and the cooling is also running on full, no extra moisture can be extracted. If 3-4 litres of water is sprayed, this will often result in discoloured mushrooms a day later and lots of fruits to be picked. This is not good for production in total, nor for quality. In this case its better not to spray, even though the casing soil will seriously dehydrate towards the end of the flush.
John Peeters, C point